Presently, an electric servo motor or a brushless motor is used to control the torque, rotational speed and angle of an electric tool or apparatus. Torque, rotational speed and angle signals from the electric tool or apparatus are detected and fed back by an encoder to an electric servo motor driver for signal analysis; and then based on the analytical results, required control formulas are encoded using mathematical programs for controlling the torque, rotational speed and angle of the electric tool or apparatus. However, in the current air tool industry, there is not any air motor with similar servo functions.
Generally, the use of an air motor is mainly based on a consideration of the working environment. The air motor are widely applied to petroleum and chemical plants, places with high concentration of dust, mineshafts, offshore oil platforms, sewers and damp environments because of the following unique advantages of the air motor: (1) no temperature rise at overload, no spark during operation, and no shock and short circuit risks; and (2) compact and light, and having higher output torque compared to an electric motor of similar volume. However, the air motor has the following disadvantages: (1) uneasy to control because air is compressible, highly frictional, tending to leak out and nonlinear; (2) not precisely controllable in its operational movements because the air motor does not stop immediately due to residual air pressure in the air supply line after the air supply is cut off; and (3) not controllable with an encoder because of its very high rotational speed of at least 6000 rpm or even more than 10000 rpm. Presently, all types of air motors have difficulty in rotational speed, rotational angle and torque controls, and are allowed only for simple switch between forward and reverse rotation. In view that there are quite many working environments in which electric servo motor is not suitable for use, the demand for products related to air motor servo control is growing rapidly.
It is therefore desirable to develop an air servo motor that can stop emergently, switch between forward and reverse rotation, increase or reduce rotational speed, operate at a specific angle, move by inching and operate at controlled torque similar to an electric servo motor.